The cresting of the gas-oil or the oil-water interface in horizontal wells is an important phenomenon in reservoir engineering. The application of horizontal well technology has shown to be attractive for reducing the gas and water production, and thus enhancing the production of oil. The production rate required for delaying gas breakthrough in horizontal wells could be improved and optimized by modeling the cresting phenomenon accurately. For modeling, a good understanding of cresting phenomena is needed to optimize oil production from horizontal wells. The objective of this work is to identify the important parameters affecting the cresting phenomena. Cresting towards a horizontal well with a gas-cap drive has been studied experimentally using scaled model prototypes packed with glass beads. Displacement rates that ranged from 0.055 m³/m/day to 96 m³/m/day were used to evaluate the critical rate of production of horizontal wells at different conditions of viscosity and permeability respectively. Results are presented for the transient and steady-state cresting behavior and the critical cresting oil production rate. The effect of capillarity on the development of the cresting phenomena and the effects of heterogeneity on the behavior of critical cresting rate are also addressed in this thesis.

A new correlation was established and successfully used to well-describe all experimental data of sweep efficiency using the prototype models in this work, as well as the Hele-Shaw model studies reported in literature. The range of applicability for critical cresting rate has been determined experimentally in this work. The analytical formulas reported in the literature for predicting the critical cresting rate were tested with experimental results and it was found that only the formulas developed by Suprunowicz and Butler (1992) and Hongen (1997) were in good agreement with our experimental data. The results of this work also show that the gas cresting phenomena at gas breakthrough depend on the dimensionless rate, q*, as well as the well spacing, porosity of the system, the capillary number (the ratio of viscous forces to capillary forces) and Bond number (the ratio of gravity forces to capillary forces) conditions. Through experimental studies on the sweep efficiency of horizontal wells at gas breakthrough, it was found that the dimensionless rate can not be used as the only correlation parameter to determine the sweep efficiency of oil recovery by gravity drainage using horizontal wells.

The mathematical formulation for describing the transient behavior of gas cresting phenomena has been presented for incompressible fluid flow condition. The evolution of the observed gas-oil interface movement during gravity drainage displacement using a horizontal well in this work was successfully simulated using the CompFlow simulator and the results obtained were in very good agreement with the experimental results for different prototype scenarios. Furthermore, the simulation results at different height-to-width ratios on field scale scenario based on the sweep efficiency correlation obtained in this work have proved the reliability of using the dimensionless variable ψ = q*/(ϕ(H/W)²) for estimating the oil recovery efficiency at gas breakthrough condition for field situations. Experimental results on the postbreakthrough behavior for both closed and an open-outer boundary system have also been presented.